Knee joint orthosis

Abstract

There is provided a knee-joint orthosis for persons whose legs are weak or unstable. The orthosis includes a first elongate member adapted to be secured along the lower leg below the knee, and a second elongate member adapted to be secured along the upper leg above the knee. The two elongate members are hinged together at a pivot location which, when the elongate members are secured to the leg, can be substantially aligned with the hypothetical pivot axis between the upper and lower leg. A tension member is secured between a first location which moves with the first member and a section location which moves with the second member, the force of the tension member acting along a line which is spaced from the pivot location and which is such that tension in the tension member increases as the leg is flexed. In this manner, the moment acting to extend the leg increases as the leg is flexed.

We claim: 
     
       1. A knee-joint orthosis for persons whose legs are weak or unstable, comprising: a first elongate member adapted to be secured along the lower leg below the knee,   a second elongate member adapted to be secured along the upper leg above the knee, the two elongate members being hinged together at a pivot location which, when the elongate members are secured to the leg, can be substantially aligned with the hypothetical pivot axis between the upper and lower leg,   and a tension member secured between a first location which moves with said first member and a second location which moves with said second member, the force of the tension member acting along a line which is spaced from the pivot location and which is such that tension in said tension member increases as the leg is flexed, whereby the moment acting to extend the leg increases as the leg is flexed,   the second location being on a cog member pivoted about said pivot location, said second location being spaced from said pivot location, the second elongate member including means for rotating the cog member along with the second elongate member about said pivot location,   said means including a dog pivoted to the second elongate member, the dog being pivotally mounted to move between (a) a first position in which it bears against said cog member and rotates the same along with the second elongate member, and (b) a second position in which it frees the cog member for movement independent of said second elongate member.   
     
     
       2. The orthosis claimed in claim 1, in which the tension member includes an elastic cord which is under pretension when the orthosis is in the position corresponding to leg extension. 
     
     
       3. The orthosis claimed in claim 1 or claim 2, which includes means restraining the two elongate members from pivoting from the extended position in the rotational sense opposite that corresponding to leg flexure. 
     
     
       4. The orthosis claim in claim 1 or claim 2, in which the two elongate members undergo mechanical interference when they are in the position corresponding to leg extension, and from such position can only mutually pivot in the direction corresponding to leg flexure. 
     
     
       5. The orthosis claimed in claim 1, which further includes control means by which a wearer of the orthosis can selectively move the dog from said first toward said second position. 
     
     
       6. The orthosis claimed in claim 5, in which said control means includes a pivotal foot brace at the bottom of the second elongate member, swingable by ankle motion, and a Bowden wire connected to allow pivotal motion of the foot brace in the direction of plantar flexion to move the dog from said first toward said second position. 
     
     
       7. The orthosis claimed in claim 1, in which the tension member includes a cable having one end connected to said cog member, the cable being entrained around a freely-rotating pulley and having its other end attached to one end of an elastic member, which in turn has its other end connected to an attachment point fixed with respect to the first elongate member and spaced below said pivot location between the elongate members.